Make the pedigree id sticky across profile sync

The dog id in the synced profile shares one last-write-wins timestamp with
name and birthday, and that timestamp comes from each device's own clock.
A device whose profile was stamped later (clock skew, or a more recent
name/birthday edit) would refuse to adopt a newer server profile that had
just gained an id, or even push its empty id back over the stored one — so
the pedigree id set on one device never reached the others.

Make the id sticky on both sides of sync: an empty value never clears a set
one, and a device/server adopts an id it is missing regardless of the blob
timestamp. When both sides have an id, the newer profile still wins, so the
dog can still be changed. Name and birthday keep plain last-write-wins.

src/changelog.json

@@ -1,4 +1,5 @@
 [
+  { "date": "2026-07-26", "text": "The pedigree ID set in Settings now syncs reliably to your other devices — it's no longer dropped when two devices' clocks disagree" },
   { "date": "2026-07-26", "text": "New 🌳 Pedigree page: add your dog's SKK chip or registration number in Settings to unlock it, then explore its ancestry as a tree — the first generations show at once and the line fills in further back as it's traced from SKK Hunddata. It's cached, so it reopens instantly and works offline" },
   { "date": "2026-07-24", "text": "The age counter reads \"16 weeks (3 months and 3 weeks) old\" so weeks and months line up; past 4 months it drops the weeks and shows just months (e.g. \"5 months and 2 weeks old\")" },
   { "date": "2026-07-17", "text": "The Sleep trend chart follows the selected day — pick a past day to see its full curve against the day before and the average leading up to it" },